The world's biggest social networking company said Wednesday that it is paying $12 billion in Facebook stock and $4 billion in cash for WhatsApp. In addition, the app's founders and employees will be restricted stock worth $19 billion that will vest over four years after the deal closes.

The deal translates to roughly 9 percent of Facebook's market value and is bigger than any acquisition made by Google, Apple or Microsoft.

"The services that reach that milestone are all incredibly valuable," Zuckerberg said.

WhatsApp, a messaging service for smartphones, lets users chat with their phone contacts, both one-on-one and in groups. The service allows people to send texts, photos, videos and voice recordings over the Internet. It also lets users communicate with people overseas without incurring charges for pricey international texts and phone calls. It costs $1 per year and has no ads.